Classification
AP BIOLOGY 11
13. The Protists
•  The protists are by far the most difficult
group of organisms to classify.
•  It is the most artificial and disagreed upon
by biologists.
•  We will not focus so much on the taxonomy
as the diversity within this group.
•  We will divide them into three groups based
upon their nutrition method.
Classification
1. Ingestive Protists
•  These are animal
like protists that
bring food into cells
(ingest) and digest
it.
•  Examples include
the Protozoa.
A Paramecium
Classification
3. Photosynthetic
Protists
•  Plant like protists that
do photosynthesis.
•  Include most of the
unicellular, colonial,
and multicellular
algae.
Classification
2. Absorptive Protists
•  Fungus like protists that
use extracellular digestion,
ie. They secrete enzymes
onto a food source, digest
it, then absorb the digested
products.
•  Ex: Water and slime
molds.
A plasmodial slime mold
Evolution
•  Protists represent the first eukaryotes.
•  Probably evolved from prokaryotes that didn’t
have a cell wall (therefore flexible).
•  Maintained shape with their cytoskeleton.
•  This could also “pull” is some plasma
membrane to surround their nuclear material forming a nucleus (by process like
phagocytosis).
1
Evolution
•  This started cytoplasmic compartmentalization
which allows for internal specialization.
•  Cytoskeleton also allowed for new mode of cell
division - mitosis.
•  This removed the restriction of one circular
chromosome, allowing many linear
chromosomes - this produces more genetic
information and more complexity.
Ingestive Protists
1. Archeozoa
•  “ancient protists”
•  Lack mitochondria
(primitive feature),
often flagellated.
•  Ex. Giardia sp.
(Beaver Fever)
•  This also allowed for true sexual reproduction to
occur with meiosis and fertilization - increasing
variations!
•  The evolution of mitochondria and chloroplasts
probably involved the evolution of a symbiotic
relationship between a prokaryote and the
evolving eukaryote.
•  Protist evolution is still quite obscure.
Ingestive Protists
2. The Flagellates
•  Move by flagella.
•  Contain both photosynthetic and
heterotrophic varieties.
•  Also contains parasitic forms.
•  Three main subgroups:
Ingestive Protists
A. Dinoflagellates
•  Photosynthetic.
•  Major component of
phytoplankton in the
ocean.
•  Cause “Red Tides”
which can cause
paralytic poisoning
when eating shellfish.
Evolution
Ingestive Protists
B. Sporozoans
•  Form spores at one
stage of life cycle, other
stage moves by flagella.
•  Ex. Plasmodium vivax
parasite that causes
malaria.
•  Learn its life cycle and
vector.
P. vivax in human blood smear
2
Ingestive Protists
C. Euglenophyta
•  Contains Euglena and
related organisms.
•  Combine auto and
heterotroph character.
•  Shows why protists are
so difficult to classify.
•  Moves by flagellum.
Ingestive Protists
3. Ciliates
•  Among most complex of
protozoans - show high
degree of intracellular
specialization.
•  Have body “systems”
like animals.
•  Reproduce sexually by
conjugation.
Paramecia
Ingestive Protists
Ingestive Protists
Ingestive Protists
Ingestive Protists
4. Rhizopoids
•  Move by pseudopods
with cytoplasmic
streaming demonstrates “sol-gel” phase reversal.
•  Includes largest
eukaryotic cells - the
amoeba.
5. Radiolaria
•  Secrete a “glass” skeleton.
•  Major component of fresh and salt water plankton.
•  Basis of aquatic food chains.
6. Forminifera
•  Have CaCO3 skeleton (chalk) form large
deposits on ocean floors.
•  Mostly marine, have pseudopods.
•  Major source of chalk (white Cliffs of
Dover).
3
Absorptive Protists
Slime Molds
•  Fungus like protist
that also has stage that
resembles ameba.
•  Most common stage
resembles a mass of
gooey fungus called
the “Plasmodium”.
Absorptive Protists
•  The plasmodium
forms an upright
sporangium that
produces and releases
haploid spores.
•  These germinate to
form the haploid
ameba like and
flagellated stages.
Absorptive Protists
•  These synapse to form a zygote which
grows back to the plasmodium.
•  The zygotes all merge together to form the
plasmodium which is the feeding stage.
•  The asexual (spore) stage is
environmentally resistant to survive winters.
Plant Like Protists: Algae
A) The Diatoms
•  Classified as “Golden
- Brown Algae”.
•  Produce glass-like
(silica based) cell
walls in “box and lid”.
•  Compose a large part
of fresh and salt water
plankton.
Plant Like Protists: Algae
•
•
•
•
Most diverse group.
Not all agree should be classified as protists
All are photosynthetic.
May be unicellular, colonial, or
multicellular (some classify these in the
plants).
Plant Like Protists: Algae
B) Brown Algae
•  Phylum Phaeophyta.
•  Contains brown
pigment “fucoxanthin”
as accessory light
pigment (masks
chlorophyll color).
•  Mostly marine and
temperate.
Kelp
4
Plant Like Protists: Algae
•  Kelp such as Macrocystis sp.
shows basic adaptation to living
near land and was necessary
precursor to evolution of plants
to land.
•  Show specialized regions: blades
for photosynthesis and
reproduction, stipe to hold and
suspend blades, air bladders to
float plant, and...
Plant Like Protists: Algae
C) Red Algae
•  Phylum Rhodophyta.
•  Red due to red
accessory pigment
(phycoerythricin).
•  Most common in
warmer tropical waters.
•  In temperate zones,
found in deeper water.
Plant Like Protists: Algae
1. Unicellular Green
Algae
•  Very common in fresh
water as part of
phytoplankton.
•  Ex. Chlamydomonas
sp.
Plant Like Protists: Algae
•  Holdfasts to enable
plant to stay anchored
in nutrient rich
continental shelf area.
•  Kelp beds provide
foundation of a major
marine ecosystem.
•  Show “Alternation of
Generations”
Holdfast of Macrocytis sp.
From Bamfield BC
Plant Like Protists: Algae
D) Green Algae
•  Phylum Chlorophyta.
•  Very diverse group.
•  Include unicellular,
colonial, and
multicellular forms.
•  Live in all
environments: fresh
and salt water, soil.
Ulva sp. Sea lettuce
Plant Like Protists: Algae
2. Colonial Green Algae
•  Live in long filaments or as
colonial spheres.
Filamentous green algae
Volvox, spherical colonial
5
Plant Like Protists: Algae
3. Multicellular Green Algae
•  Mostly marine.
•  Likely ancestors of land
plants.
•  Show equal Alternation of
Generations (a pre-adaption to
land) with equal Sporophyte
and Gametophyte.
•  (end show)
6